In fiber-optic communications, wavelength-division multiplexing (WDM) is used to multiplex a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light. A WDM system uses a multiplexer at the transmitter to join a plurality of signals together, and a demultiplexer at the receiver to split them apart.
One benefit of implementing WDM in an optical system is that it allows the capacity of an optical communications network to be increased without laying more fiber. Thus, new technology can be implemented in an optical infrastructure without having to overhaul the backbone network. The capacity of a given link can be expanded simply by modifying or upgrading the multiplexers and demultiplexers at each end.
Different WDM systems use different wavelength patterns to implement a plurality of communication channels in an optical fiber. The different systems are referred to either as Conventional, or Coarse, WDM (CWDM) and Dense WDM (DWDM). WDM systems that provide up to 8 channels per fiber are referred to as CWDM, and systems that provide more channels per fiber are referred to as DWDM. DWDM systems typically provide 40 channels or 80 channels per fiber. The number of channels that can be accommodated per fiber is determined by channel spacing. Wide spacing allows the use of less sophisticated, and therefore less expensive, transceivers. Herein, both CWDM and DWDM technologies are referred to collectively simply as WDM.
Network systems in general can be described in terms of a networking model promulgated by the Open Systems Interconnection effort at the International
Organization for Standardization, the so-called “OSI model”. The OSI model characterizes the functions of a communications system in terms of logical layers called abstraction layers. A layer serves the layer above it and is served by the layer below it, and various communication functions are grouped into the various layers. The OSI model is summarized in FIG. 1. As shown in the figure, layer 1 (L1) is called the Physical layer, and describes the physical media over which communication signals are propagated, as well as a description of the signal and binary transmission parameters. Layer 2 (L2) is called the Data Link layer, and describes datagram addressing. Layer 3 (L3) is called the Network layer, and its functions include path determination and logical addressing of messages in a communication channel. Collectively, L1, L2, and L3 are referred to as the media layers.
In this context, a communications protocol is a system of digital message formats, and rules for exchanging the messages in or between devices in telecommunications. The protocols may include signaling, authentication, error detection, and correction capabilities. The Internet Protocol (IP) is a communications protocol used for relaying datagrams (network packets) across a network, and is responsible for routing packets across network boundaries in an internetwork.